I. Field of the Invention
This invention relates generally to metallic and intermetallic matrix composite materials such as titanium alloy matrix composites, and more particularly to fiber infiltrated and reinforced titanium alloy metal matrix composites which exhibit the combined properties of high strength and stiffness at elevated temperatures, good ductility, and good resistance to matrix cracking.
II. The Prior Art
Various types of power turbine engine components are conventionally fabricated from different kinds of steel, nickel and titanium alloys. In use, these components are typically subjected to rather severe environmental conditions which require the components to have a combination of diverse properties generally not found within most individual materials. To overcome this type of problem in the gas turbine industry, hybrid metal and composite components, such as for example shafts, have been constructed. Following the example of a shaft, this component must withstand the torsional and bending stresses typically placed on small diameter drive shafts used in a turbine engine. Fully consolidated hybrid shaft can be produced having a metal outer shell, e.g. steel or nickel, and a metal matrix composite inner sleeve, e.g. titanium matrix composite. However, such production is time-consuming and requires bonding these materials together, introducing the possibility of failure of the material during use by fracture.
Titanium alloys are among the more desirable structural materials useful for manufacturing a component for a gas turbine. This is because titanium alloys have the combination of high strength and low density. However, generally speaking, commercially available alloys are limited in use to lower temperature ranges (below about 800.degree. F.) because of decreasing creep strength and oxidation resistance at elevated temperatures. At the higher temperature ranges (above about 1000.degree. F.) higher density materials such as iron, nickel and cobalt base superalloys have been used. However, it is still desirable to use the lightweight titanium base material at elevated temperatures because the lower weight of titanium reduces the amount of stress on the material when the material forms a rotating component.
The prior art presently discloses a wide variety of various metal matrix composite materials exhibiting a wide variety of properties. Some specific examples of these prior art disclosures are as follows:
U.S. Pat. No. 3,427,185 to Cheatham, et al. discloses a composite structural material incorporating metallic filaments in a matrix. The metal matrix material has a melting point higher than the recrystallization temperature of the filamentary material and is deposited thereon by plasma and spraying.
U.S. Pat. No. 3,455,662 to Alexander, et al. discloses a high strength whisker reinforced metallic monofilament wherein the whiskers are aligned in the elongate direction of the monofilament. The whiskers are present in the form of a roving with the metal matrix applied by electroplating, vapor deposition or the like. Suitable whisker materials are the metallic and non-metallic oxides, carbides, nitrides, silicides and borides.
U.S. Pat. No. 3,556,837 to Hammond discloses a composite of a plurality of pairs of alternating layers made by vapor deposition of materials wherein one is ductile relative to the other. One layer is referred to as a high strength "fibrous" material while the other is a ductile matrix material. Suitable fibrous materials include boron, carbon, silicon, beryllium and the refractory metals as well as ceramic compounds and the carbides, borides, nitrides and silicides thereof. Suitable ductile materials include aluminum, beryllium, magnesium, scandium, iron, nickel, copper, titanium and the like. No disclosure of titanium alloys is made.
U.S. Pat. No. 3,691,623 to Staudhammer, et al discloses a process for increasing the whisker and fiber content in a matrix wherein layers of whiskers aligned on a similar metal substrates are stacked into a preform assembly and diffusion bonded to consolidate the preforms into a composite foil. Various materials are suitable as both the whiskers and the matrix.
U.S. Pat. No. 4,010,884 to Rothman discloses a method of fabricating a filament-reinforced composite article comprising monolayer boron fiber tapes and laminates of titanium. The boron fibers are attached to an aluminum foil which is interleaved with titanium and diffusion bonded at a temperature below the melting temperature of the aluminum to bond the fibers in a matrix of aluminum and titanium. This disclosure is different from the invention described herein in many ways. First, the Rothman disclosure is limited to and depends on combinations of aluminum and titanium. Second, the Rothman disclosure specifically describes that the fabrication temperature of the composite must not exceed 1050.degree. F. or the melting temperature of aluminum. The fabrication temperature of the composite described by the present invention must exceed 1050.degree. F. in view of the materials used in the composite. Third, it appears that the utilization temperature of the composites described by Rothman must be well below 1050.degree. F., and most probably in the range of 400.degree. F. to 500.degree. F. On the other hand, the composite described by the present invention is aimed at utilization temperatures in the range of about 1500.degree. F. maximum.
U.S. Pat. No. 4,141,802 to Duparque, et al discloses fiber reinforced metal panels and the production thereof wherein the panels comprise a metal substrate onto which is sprayed or electro deposited a metal bonding layer and a layer of reinforcing fibers. A thin layer of metal matrix is sprayed over the fibers to penetrate them and melt the bonding layer and bond it to the metal substrate.
U.S. Pat. No. 4,499,156 to Smith, et al., discloses titanium metal matrix composites wherein the titanium alloy has high strength and at least 40% beta phase. High stiffness filaments, such as silicon carbide or the like are embedded in the composite, formed by diffusion bonding and producing substantially reduced reaction zones.
The most common problems encountered with titanium alloy composites produced by prior known heat pressure lamination methods and with prior used reinforcing filaments, relate to the uneven or non-uniform, non-integral interfacial filamentary layer formed between the high strength titanium alloy layers. This is due to the fact that coarse unidirectional fabrics of relatively thick fibers must be used in order to permit the alloy layers to penetrate between the fibers during diffusion bonding. Thick fibers, i.e., having a diameter of about 0.15 mm or greater, are too stiff to weave into a multidirectional fabric, and composites of such thick fibers cannot be shaped. Thinner filaments, i.e, having a diameter of about 0.03 more less and preferably between about 0.01 and 0.02 mm, are sufficiently flexible to be woven into multidirectional fabrics, and such fabrics are sufficiently flexible or limp in all directions to permit shaped composites to be formed therefrom. However attempts to integrate such thin fibers and fabrics between titanium alloy layers by heat and pressure lamination are not satisfactory unless temperatures are used which melt the titanium alloy sufficiently to permit it to flow into the small intersitices between the thin fibers of the fabric which has a close weave due to the small diameter of the filaments. However such melting temperatures destroy the strength of the filaments, and lower temperatures do not allow the titanium alloy to infiltrate the filamentary layer or to penetrate and bond to the adjacent titanium alloy layers.
Interposed layers of other metals, such as aluminum, in association with the desired thin filaments and fabrics do not produce satisfactory bonding results, even at temperatures high enough to melt the aluminum, since the aluminum layer does not integrate with the unmelted titanium alloy layers to form an integral high-strength composite product.